Antarctic

Description

A vast, icy continent at the very south of the planet, the Antarctic is a land of extremes. Larger than Europe and nearly twice the size of Australia (1)(2), it is almost entirely buried beneath an ice sheet which covers around 99 percent of the land surface (2)(3)(4). The Antarctic ice sheet contains 90 percent of the world’s ice and around 70 percent of its freshwater (2)(3)(5)(6)(7).

The Antarctic is the world’s coldest continent, holding the record for the lowest temperature ever recorded on the Earth’s surface, at -89.2 degrees Celsius (1)(3)(6).

Antarctic fact file

Description

A vast, icy continent at the very south of the planet, the Antarctic is a land of extremes. Larger than Europe and nearly twice the size of Australia (1)(2), it is almost entirely buried beneath an ice sheet which covers around 99 percent of the land surface (2)(3)(4). The Antarctic ice sheet contains 90 percent of the world’s ice and around 70 percent of its freshwater (2)(3)(5)(6)(7).

The Antarctic is the world’s coldest continent, holding the record for the lowest temperature ever recorded on the Earth’s surface, at -89.2 degrees Celsius (1)(3)(6). The mildest areas are around the coasts and in the continent’s most northerly region, the Antarctic Peninsula, where temperatures can sometimes rise to slightly above freezing in summer and generally average around -10 to -30 degrees Celsius in winter (1)(3)(5). In the highest parts of the continent’s interior, summer temperatures rarely exceed -20 degrees Celsius and often fall below -60 degrees in winter (1)(3).

Due to the Antarctic’s position at the South Pole, the long Antarctic winter is spent in continuous darkness, while in mid-summer parts of the continent experience 24 hours of sunlight (2)(6)(8).

With an average elevation of 2,500 metres, the Antarctic is the highest of the world’s continents (1)(4). Its ice sheet is over 4 kilometres thick in places (1)(4), and hides spectacular mountain ranges, as well as valleys and even lakes. Only the highest mountains and a few isolated peaks of rock, known as ‘nunataks’, show above the ice (1)(2)(3). Cold, dense air from the Antarctic’s high interior flows downhill towards the coast, resulting in some of the windiest conditions on Earth (1). Known as ‘katabatic winds’, these winds can exceed speeds of 100 kilometres per hour for days at a time, with some gusts reaching over 320 kilometres per hour (1)(6)(9).

Perhaps surprisingly, the Antarctic is also the driest continent on Earth. Most precipitation falls at the coast, while the interior of the continent is classified as a polar desert, receiving as little as 50 millimetres of precipitation a year. Most of this falls as snow, which builds up over time and is gradually compressed into ice. This ice slowly flows towards the coast in the form of numerous glaciers, and extends out over the sea, forming floating ‘ice shelves’ that eventually break up into icebergs (1)(3)(4)(6)(9). In places, the Antarctic ice sheet is so heavy that the underlying land has been pushed below sea level (3)(5)(6).

In winter, the sea around the Antarctic coast freezes to form salty ‘sea ice’, more than doubling the ice-covered area of the continent (1)(2)(3)(4)(6)(9). In summer, the sea ice is mainly confined to areas such as the Weddell Sea and Ross Sea (1).

The Antarctic continent is surrounded by the Southern Ocean, an extension of the southernmost parts of the Atlantic, Pacific and Indian Oceans. The Southern Ocean is generally defined as the area south of the ‘Antarctic Convergence’, where cold Antarctic waters meet warmer waters to the north (2)(6)(8)(9)(10). A relatively deep ocean, it is characterised by strong winds and a current that flows from east to west around Antarctica, known as the Antarctic Circumpolar Current (2)(9). The interactions between these winds and currents, together with the presence and melting of sea ice, have significant effects on global climate and ocean circulation patterns (1)(3)(5)(6)(7)(9).

Terrestrial life in the cold, inhospitable environment of the Antarctic is mainly confined to the few areas of exposed, ice-free rock, mostly around the coast and in the slightly more temperate Antarctic Peninsula. Vegetation cover is largely limited to mosses, lichens and algae, while animal life consists of a few small insects and other invertebrates, together with breeding colonies of seals and penguins (1)(2)(3)(5)(8). In contrast, the oceans around the Antarctic support a rich marine ecosystem. Its waters are rich in nutrients and oxygen, producing abundant plankton which in turn supports a variety of marine species, from tiny krill to a range of fish, seals, whales and seabirds (2)(6)(8)(9). Many Antarctic species show unique adaptations to their harsh environment (2)(3)(6).

Surrounding Antarctica are a number of Antarctic and sub-Antarctic islands, which range in size from small clusters of rocks to larger islands, and which support a rich variety of wildlife. Some of these islands are almost completely covered in ice (1)(3), while others, such as Macquarie Island, are ice-free and have no permanent covering of snow (1).

Range

Located at the southernmost part of the Earth, Antarctica is a large continent that covers an area of almost 14 million square kilometres (1)(3)(6)(8)(9). The continent is largely divided into two parts, known as East Antarctica and West Antarctica, by one of the world’s longest mountain chains, the Transantarctic Mountains (1)(3)(6)(9). The highest of Antarctica’s mountains is the Vinson Massif, which reaches an elevation of 4,897 metres above sea level (1)(3).

The Antarctic is also home to the planet’s southernmost active volcano, Mount Erebus, which is unusual in being one of only three volcanoes in the world to have a permanent lake of molten lava (8).

Further north, the Antarctic and sub-Antarctic islands include South Georgia, a long, narrow, mountainous island some 1,300 kilometres south of the Falkland Islands (11)(12), as well as the South Sandwich Islands (11), Macquarie Island, Heard Island and the McDonald Islands, the Auckland, Campbell and Snares Islands, and the French Southern and Antarctic Lands (4)(9)(13)(14)(15).

Most of the terrestrial plant life of the Antarctic consists of lower plant groups, such as mosses, liverworts and lichens. Lichens and some mosses can be found growing even on windswept, dry rock surfaces, and are well adapted to survive the harsh climate (1)(2)(3). A number of fungi species are also found in the Antarctic (1)(3).

Although poor in higher plants, the Antarctic does support single-celled algae, which grow both on land and in the ocean, where they contribute to the ‘phytoplankton’ that are an important part of the marine food chain (1). Algae can even be found growing on ice and snow (1)(2), often colouring it red, green or orange (1).

The milder, wetter sub-Antarctic islands are more suitable for plant growth, and most have a slightly more diverse range of flowering plants and ferns (3)(5)(13)(14)(16). These include tussock grass, a tall, robust plant which often forms the tallest vegetation cover (3)(14). Human activities on these islands have also led to many non-native plant species being introduced (3)(16).

Most whale species around Antarctica are migratory, moving north to warmer waters in winter to give birth, and returning again in the spring to feed in the rich waters of the Southern Ocean (1)(3)(6).

Although the sub-Antarctic islands also lack native land mammals, humans have introduced a variety of non-native species, including rats, mice, cats, rabbits, sheep and reindeer, often with damaging impacts on native species (3)(4)(9)(14)(17).

There are around 200 fish species in the Antarctic region (2)(4), most of which are slow-growing and have unique adaptations to the cold (2). The majority of Antarctic fish come from the Nototheniidae family, commonly known as the Antarctic cods, which includes species such as Notothenia nudifrons and Notothenia coriiceps(2)(3)(4). Many of these species possess ‘antifreeze’ substances in their blood (1)(2)(3)(4)(9).

The terrestrial invertebrate fauna of the Antarctic continent is relatively poor, consisting mainly of species such as springtails, mites and nematode worms (1)(2)(3). However, the population densities of these species can often be high (3). On the milder sub-Antarctic islands, a range of other species can be found, including spiders, beetles, earthworms and flies (1)(3).

Large numbers of squid are also found around the Antarctic, including the large giant squids of the genusArchiteuthis(2)(3). The squid in turn provide food for a range of predators, from seabirds to sperm whales.

Perhaps the most important species in the Antarctic is the Antarctic krill (Euphausia superba). This small, shrimp-like crustacean lives in dense swarms and is one of the most abundant and successful animals on the planet. Despite its small size, krill is vital to the Antarctic food chain, providing the staple food for a wide range of fish, whales, seals, penguins and seabirds (1)(2)(3)(4)(9).

Threats

A remote, hostile wilderness, the Antarctic remains the most uninhabited continent on Earth, only visited by scientists and tourists (3)(4). However, its fragile and increasingly vulnerable environment has not been unaffected by human activities (1)(3)(5).

The wildlife of the Antarctic has been exploited for many years. Humans were first attracted to the Antarctic by the region’s whales and seals, and many species were severely overexploited (1)(3)(6)(18). Although now largely protected, some of these species will take time to recover from previous declines (3)(6), and may face further threats from marine pollution, disturbance by tourists, competition and interactions with fisheries, and the effects of climate change (18).

Many of the Antarctic’s seabirds are also under threat, mainly from accidental mortality caused by longline fisheries, which use lines of baited hooks on which foraging seabirds can get caught (1)(3)(5). Further threats include pollution, depletion of fish and krill stocks by fisheries, and environmental changes potentially linked to climate change (1)(5). Some penguin populations have also shown large declines, possibly linked to reduced food supplies and changes in sea ice (5).

Introduced, non-native mammals have also had devastating effects on seabird colonies, with rats and cats killing chicks on a number of sub-Antarctic islands (4)(11)(12)(16). On South Georgia, the presence of rats is also driving the endemic South Georgia pipit to extinction, and this species now breeds only on rat-free offshore islands and islets (12)(16).

In addition to introduced predators such as rats and cats, non-native grazing animals such as reindeer and rabbits are destroying native vegetation and altering habitats on many sub-Antarctic islands, while introduced, non-native plants are also spreading (9)(14)(16)(17). The remoteness and harsh climate of the Antarctic continent have largely limited the impact of introduced species. Some invertebrate and plant introductions have occurred, but these species have not yet become established (3).

Commercial fishing in the Southern Ocean only began in the 1960s, but was unregulated for the first few decades, resulting in large declines in species such as the marbled rockcod (Notothenia rossii) (1)(3). Fishing regulations are now in place, with the main target species being the Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni) (3)(5). However, illegal, unreported and unregulated fishing is still a problem, and undermines efforts to manage fish stocks. Illegal fishing vessels often use destructive fishing techniques, and do not implement measures intended to reduce seabird mortality caused by fishing gear (1)(5)(10).

A developing fishery for krill is also of concern (3). Krill species are increasingly in demand, sometimes for human food products, but more commonly to make feed for farmed fish and for use in nutritional supplements (1)(2)(4)(5). Krill populations have been declining (5), and the krill harvest will need to be carefully regulated if it is not to have severe impacts on the entire Antarctic marine ecosystem (2).

More localised human impacts in the Antarctic include pollution and disturbance to wildlife caused by scientists and other visitors, although strict regulations are now in place to minimise environmental damage (1)(3). Oil spills remain a potential risk (1)(6), and there is concern that the growing number of tourists visiting the region could negatively affect the Antarctic environment (1)(3)(5)(6).

Although oil prospecting and mineral extraction have been banned in the Antarctic (1)(3)(5)(6)(19), ‘biological prospecting’ (investigating the unique properties of Antarctic species for use in commercial or medical products) could potentially become a threat (5)(19). There is also debate about whether scientists should drill into lakes under the ice, such as Lake Vostok, a huge lake over 3,000 metres below the ice. The water in these lakes may be millions of years old, and there are fears that drilling equipment could contaminate this unique and pristine environment (4).

Perhaps the greatest future threat to the Antarctic is global climate change. The Antarctic is vital to many global processes, including water circulation and the uptake of carbon dioxide by the world’s oceans. Environmental changes in the Antarctic could therefore have repercussions around the world (1)(6)(7). Although the effects of climate change in the Antarctic are complex and not fully understood, current models predict that, at current rates, melting of the ice sheet in West Antarctica could contribute to sea level rise of up to 1.4 metres by 2100 (7).

On a more local scale, a reduction in winter sea ice could mean icebergs are more free to drift, causing greater damage to sea bed communities from scouring by ice (20). Increased water temperatures are also likely to alter marine communities (1). For example, king crabs (Neolithodes yaldwyni), a predatory species, are already moving onto the Antarctic shelf and are likely to have significant impacts on other species (21). On land, increased melting is likely to expose new land for colonisation by plants and animals (1)(7).

Increasing levels of ‘greenhouse gases’ such as carbon dioxide, which are believed to be driving global climate change, are also leading to increased ocean acidity. This is a particular problem in the Southern Ocean, as cool water absorbs more carbon dioxide than warmer waters. Increased acidity may affect the ability of marine organisms to form their shells, and so is likely to impact on species such as crustaceans and corals (1)(5)(7).

One of the most significant scientific discoveries in the Antarctic has been the presence of the ‘ozone hole’, a dangerous thinning of the ozone layer in the Earth’s upper atmosphere, caused by the use of chlorofluorocarbons (CFCs). This hole potentially increases the amount of damaging UV radiation reaching the Antarctic region, and may have a significant effect on the Antarctic climate (1)(3)(7).

Conservation

The Antarctic is one of the best protected areas in the world (3). Many nations undertake scientific research in the region, much of which is aimed at better understanding the Antarctic’s unique ecosystems and the effects of climate change (1)(3). There are also many organisations involved in its protection (5).

Some parts of the Antarctic receive extra protection in the form of Antarctic Specially Protected Areas (ASPAs), Antarctic Specially Managed Areas (ASMAs), or as Historic Sites and Monuments (HSMs). These protected areas often require permits to enter, and activities within them are governed by management plans and require environmental impact assessments (1)(3)(6)(19). There are currently few Marine Protected Areas in the Antarctic, and efforts are underway to identify those areas of the ocean needing particular protection (1)(3)(5).

Many sub-Antarctic islands are also protected. For example, Macquarie Island, the New Zealand Sub-Antarctic Islands, Heard Island and the McDonald Islands are designated as World Heritage Sites (1)(13)(14)(15)(22), and a number of islands are covered by management plans and a range of conservation projects, such as rat eradication programmes (11)(12)(13)(14)(15)(16)(22).

Although tourism in the Antarctic is currently unregulated, most tour operators visiting the region are members of the International Association of Antarctica Tour Operators (IAATO), which aims to ensure safe and environmentally responsible tourism practices (23).

The whole of Antarctica is covered by the Antarctic Treaty, which aims to ensure that the continent continues to be used for peaceful purposes, promotes scientific cooperation, and sets aside territorial disputes between nations (19). The Antarctic Treaty includes a number of international agreements, including protection for seal species under the Convention for the Conservation of Antarctic Seals (CCAS) (1)(3)(6)(19). Fishing is regulated by the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR), which takes into account potential impacts on other species, such as whales, seals and seabirds (1)(3)(5)(6)(10)(19). Projects are also underway to protect Antarctic krill (5).

The Antarctic Treaty also includes The Protocol on Environmental Protection to the Antarctic Treaty, also known as the ‘Madrid Protocol’. This sets out strict regulations for the protection of the Antarctic environment, including the banning of mineral extraction, and regulations covering waste disposal, the introduction of non-native species, and the protection of wildlife. Environmental impact assessments are required before any activity can take place in the Antarctic, and the entire continent is designated as a “natural reserve, devoted to peace and science” (1)(3)(5)(6)(19). Many individual nations also have their own legislation covering activities and environmental protection in the Antarctic (3).

Further conservation efforts for Antarctic species include a range of measures to reduce seabird mortality in fisheries (1)(3)(5), as well as a recovery plan for the Subantarctic fur seal (Arctocephalus tropicalis) and southern elephant seal (Mirounga leonina) (18). The ‘Agreement on Conservation of Albatrosses and Petrels’ (ACAP) also seeks to conserve albatross and petrel species (24). The Southern Ocean is now designated as a whale sanctuary, protecting the summer feeding grounds of an estimated 80 to 90 percent of the world’s whales. Commercial whaling is banned, although Japan still continues whaling under the guise of scientific research (1)(5)(6).

An extreme and unique continent, the Antarctic is important to our understanding of many of the planet’s most vital systems and our impact upon them. Its ice sheets hold records of the Earth’s past climate, aiding our understanding of current climate changes. Many of the region’s species are also sensitive indicators of global change, providing an early warning of the potential impacts of threats such as climate change (1)(3)(4)(7). Understanding these changes will be key to ensuring that the unique biodiversity of the Antarctic is preserved, and that measures can be taken to combat global environmental change (1).

Glossary

simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.

Amphipods

a group of small shrimp-like crustaceans that includes sandhoppers, beach hoppers, and water lice.

Cetacean

a whale, dolphin or porpoise.

Crustaceans

diverse group of animals with jointed limbs and a hard chitinous exoskeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Echinoderms

a group of marine animals that usually have a spiny skin. This group includes starfish, sea urchins and sea cucumbers.

Endemic

a species or taxonomic group that is only found in one particular country or geographic area.

Genus

a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

a composite organism made up of a fungus in a co-operative partnership with an alga. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. Characteristically forms a crustlike or branching growth on rocks or tree trunks.

Molluscs

a diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.

Phytoplankton

aquatic plants, usually tiny, that drift passively with water movements.

Plankton

aquatic organisms, usually tiny, that drift passively with water movements; may be phytoplankton (plants), zooplankton (animals), or other organisms such as bacteria.

Subspecies

a population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.

Vertebrates

animals with a backbone, including mammals, birds, reptiles, amphibians and fish.

Smith, C.R., Grange, L.J., Honig, D.L., Naudts, L., Huber, B., Guidi, L. and Domack, E. (2011) A large population of king crabs in Palmer Deep on the west Antarctic Peninsula shelf and potential invasive impacts. Proceedings of the Royal Society B - Biological Sciences, published online 7 September 2011.

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